[PATCH v2] drm: property: use kzalloc_flex

[Rosen Penev]

Store the property values as a flexible array member instead of a
separately allocated array. This removes an allocation and its error
handling.

Add __counted_by for extra runtime analysis. Move the counting variable
assignment to right after allocation as required by __counted_by.

struct drm_property now ends in a flexible array, so move it to the end
of struct drm_damage_mock in the damage helper KUnit test to avoid
-Wflex-array-member-not-at-end.

Assisted-by: LLM
Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
---
 v2: move test struct member
 drivers/gpu/drm/drm_property.c                 | 14 ++------------
 drivers/gpu/drm/tests/drm_damage_helper_test.c |  2 +-
 include/drm/drm_property.h                     | 16 ++++++++--------
 3 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/drm_property.c b/drivers/gpu/drm/drm_property.c
index f38f2c5437e6..a6008e5c2b58 100644
--- a/drivers/gpu/drm/drm_property.c
+++ b/drivers/gpu/drm/drm_property.c
@@ -107,25 +107,18 @@ struct drm_property *drm_property_create(struct drm_device *dev,
 	if (WARN_ON(strlen(name) >= DRM_PROP_NAME_LEN))
 		return NULL;
 
-	property = kzalloc_obj(struct drm_property);
+	property = kzalloc_flex(*property, values, num_values);
 	if (!property)
 		return NULL;
 
+	property->num_values = num_values;
 	property->dev = dev;
 
-	if (num_values) {
-		property->values = kcalloc(num_values, sizeof(uint64_t),
-					   GFP_KERNEL);
-		if (!property->values)
-			goto fail;
-	}
-
 	ret = drm_mode_object_add(dev, &property->base, DRM_MODE_OBJECT_PROPERTY);
 	if (ret)
 		goto fail;
 
 	property->flags = flags;
-	property->num_values = num_values;
 	INIT_LIST_HEAD(&property->enum_list);
 
 	strscpy_pad(property->name, name, DRM_PROP_NAME_LEN);
@@ -134,7 +127,6 @@ struct drm_property *drm_property_create(struct drm_device *dev,
 
 	return property;
 fail:
-	kfree(property->values);
 	kfree(property);
 	return NULL;
 }
@@ -447,8 +439,6 @@ void drm_property_destroy(struct drm_device *dev, struct drm_property *property)
 		kfree(prop_enum);
 	}
 
-	if (property->num_values)
-		kfree(property->values);
 	drm_mode_object_unregister(dev, &property->base);
 	list_del(&property->head);
 	kfree(property);
diff --git a/drivers/gpu/drm/tests/drm_damage_helper_test.c b/drivers/gpu/drm/tests/drm_damage_helper_test.c
index 0df2e1a54b0d..c0da8dc591a9 100644
--- a/drivers/gpu/drm/tests/drm_damage_helper_test.c
+++ b/drivers/gpu/drm/tests/drm_damage_helper_test.c
@@ -17,10 +17,10 @@ struct drm_damage_mock {
 	struct drm_device device;
 	struct drm_object_properties obj_props;
 	struct drm_plane plane;
-	struct drm_property prop;
 	struct drm_framebuffer fb;
 	struct drm_plane_state state;
 	struct drm_plane_state old_state;
+	struct drm_property prop;	/* has a flexible array, must be last */
 };
 
 static int drm_damage_helper_init(struct kunit *test)
diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
index aa49b5a42bb5..8c7cef4418c4 100644
--- a/include/drm/drm_property.h
+++ b/include/drm/drm_property.h
@@ -175,14 +175,6 @@ struct drm_property {
 	 */
 	uint32_t num_values;
 
-	/**
-	 * @values:
-	 *
-	 * Array with limits and values for the property. The
-	 * interpretation of these limits is dependent upon the type per @flags.
-	 */
-	uint64_t *values;
-
 	/**
 	 * @dev: DRM device
 	 */
@@ -195,6 +187,14 @@ struct drm_property {
 	 * enum and bitmask values.
 	 */
 	struct list_head enum_list;
+
+	/**
+	 * @values:
+	 *
+	 * Array with limits and values for the property. The
+	 * interpretation of these limits is dependent upon the type per @flags.
+	 */
+	uint64_t values[] __counted_by(num_values);
 };
 
 /**
-- 
2.56.0